The advent of silicon waferboard technology has provided the vehicle by which accurate, passive alignment of optical components, both passive and active, can be accomplished with the additional benefit of reduced cost. The use of silicon bench technology to produce optoelectronic modules is disclosed in U.S. Pat. No. 4,904,036 to Blonder, incorporated herein by reference. Blonder discloses the use of a single crystal semiconductor base on which are mounted optoelectronic chips to create a modular transceiver, for example. Blonder discloses the use of v-grooves for holding optical waveguides and chips in well defined positions. The etching process to create the v-grooves is mature, and is disclosed for example in U.S. Pat. No. 4,210,923 to North, incorporated herein by reference. The Blonder further discloses the integral formation of silica waveguides on the base of monocrystalline material by chemical vapor deposition. Finally, the Blonder reference discloses the use of a waveguide to couple the evanescent wave of the main waveguide to a photodiode to monitor assembly functions or circuit operations. U.S. Pat. No. 4,989,935 to Stein, incorporated herein by reference, is another example of the fabrication of an optoelectronic device on a silicon wafer. The Stein reference discloses the use of a silicon wafer to forman integral optoelectronic transceiver with a laser chip functioning as a source and an optical receiver, a Schottky barrier diode. Further disclosed in the Stein reference is a wavelength multiplexer/demultiplexer which functions as a wavelength selective beamsplitter in the transceiver function. Finally, v-shaped grooves formed by anisotropic etching and dielectric waveguides formed on the silicon are also disclosed. Shown in FIG. 1 are the key components of a typical rare earth doped fiber amplifier. Generally the components of this type of amplifier are in bulk form, and the circuit is connected with a glass optical fiber to effect optical signal amplification. The particular example shows input optical isolator, output optical isolator 2, forward and reverse pump lasers 3 and 4. Wavelength division multiplexers (WDM's) for coupling pump laser into a common waveguide as well as for filtering residual pump energy from input and output leads are also shown. Finally, tap couplers 5 for monitoring the pump laser power and tap coupler 6 for monitoring amplifier power output power are shown in this amplifier circuit. The use and function of each of these components will be discussed herein. To effect the amplification of an optical signal in a rare earth doped fiber amplifier, the input signal to be amplified is chosen to be between 1520 and 1580 nm. This is the frequency range emitted from the stimulated emission of the coiled length of the erbium doped fiber 7. To effect stimulated emission, a signal from the pump laser 3 is chosen to be either 980 nm or 1480 nm from an appropriate source. The input signal is multiplexed with this pump signal, and then fed into the erbium doped fiber. The pump signal excites electrons in a lower energy state in the doped fiber to a higher state. In time this would effect the population inversion needed to permit lasing, in a proper laser cavity. Population inversion is achieved by pumping to excite electrons to a higher state. The electrons then decay rapidly to a metastable state (in many cases) with a longer lifetime, thereby enabling the required inversion. In an amplifier, this inversion is not utilized n the same way as in a laser, but rather is utilized to effect a more precise amplification frequency. This is clear from a consideration of Heisenberg Uncertainty, where the longer lifetime (greater uncertainty) makes the uncertainty in the energy (and hence the uncertainty in frequency) smaller. The input signal is then chosen to effect the stimulated decay of higher state electrons to a lower energy state. These quanta of light created by stimulated emission are of the same frequency and phase as the input wave, and thereby serve to amplify the input wave by constructive interference. This coherence effect is due to the coupling effect of the incident light pulse with the electrons in excited states in the doped fiber. The emitted photons are of the same direction of propagation as well. It is precisely this coherence of phase, frequency and direction of propagation that makes this kind of amplifier feasible. However, through the process of pumping and the introduction of the input signal to the erbium doped fiber, spontaneous emission occurs. Spontaneous emission of photons in the amplifying modes can adversely affect the amplification of the input signal through the introduction of noise. This noise is due to the fact that quanta of light emitted in the spontaneous emission will be of random phase and propagation direction. This light will destructively interfere with the light emitted through stimulated emission, and reduce the overall performance of the amplifier. Coherence is useful for various reasons. The first reason is that coherence makes feasible a greater variety of modulation and detection techniques, thus providing the system designer with more options. Coherent communication systems have a greater potential for better performance than do incoherent systems. For phase and frequency modulation, coherence is critical. Coherent detection techniques, for example heterodyning, require the phase of the received carrier and that of the local oscillator to be well defined and stable, so both light waves must be of a great degree of coherence. Clearly, it is of great importance to minimize as much as possible the spontaneous emission of light. For further details on the use of a rare earth doped fiber to effect amplification of an optical signal, see U.S. Pat. No. 5,056,096, incorporated herein by reference.
However, optical data transmission systems can differ greatly in their required components. As a consequence, for certain applications, the components shown in FIG. 1 may be necessary for some systems, and not needed for others. Often, an amplifier will require a single pump laser. The pump and signal may either be copropagating or counterpropagating, as determined by the relative importance of signal to noise ratio and output power requirements. Further, applications may not require two optical isolators, or, in some instances, even a single isolator, depending on the magnitude of signal reflections. System level design requirements can be established that can eliminate one or both of the isolators. In a similar manner, the use of a WDM to remove residual pump power is also a system consideration, and in some instances, such a pump filter may not be necessary. Finally, an output tap coupler is likewise a system issue, which for many signal branching applications will either not be required, or could be accomplished by other means. What is desired is a modular type device that incorporates the essential devices to effect amplification of via a gain medium such as a rare earth doped fiber, virtually independent of particular system requirements. FIG. 2 show the schematic of those components which are common to all designs of amplifiers. Specifically, the pump laser 23 is monitored by a tap coupler 25, and a WDM efficiently couples the input and pump signal to the gain medium (not shown).
What is needed is a multi-functional module that has formed or mounted thereon the essential components needed for optical amplifier systems. Such a device would allow the use of a such a module in a variety of applications, thereby enabling interchangeability as well as versatility, a worthwhile "off-the-shelf" consideration.